This invention relates to a process for the production of new, urethane-modified polyisocyanate compositions.
The production of urethane-modified polyisocyanates (i.e. isocyanate-terminated prepolymers or semiprepolymers) particularly those based on polyisocyanates or polyisocyanate mixtures of the diphenylmethane series (4,4'-diisocyanatodiphenylmethane, mixtures thereof with 2,4'- and, optionally, 2,2'-diisocyanatodiphenylmethane or phosgenation products of aniline/formaldehyde condensates which, in addition to these diisocyanates, contain higher homologs thereof), and a variety of different polyhydroxyl compounds is known. Such polyisocyanates are described, for example, in European Patent Application Nos. 10,850 and 66,130; German Offenlegungsschriften Nos. 2,347,207, 2,404,166, 2,513,793, 2,513,796, 2,620,222, 2,622,104, 2,732,182, 2,737,338, 2,804,375, 2,810,596, 2,815,579 and 2,913,126; U.S. Pat. Nos. 3,644,457, 4,055,548, 4,234,714 and 4,321,333 and also British Pat. No. 1,369,334.
In general, the processes described in these prior publications are concerned with the liquefaction of diisocyanatodiphenylmethane, more particularly 4,4'-diisocyanatodiphenylmethane, which is solid at room temperature or with a reduction in the tendency towards crystallization during storage at low temperatures of polyisocyanate mixtures of the diphenylmethane series which are liquid at room temperature.
The use of hydantoin derivatives in polyisocyanate chemistry is also known. U.S. Pat. No. 3,928,289 describes the use of hydantoin containing hydroxyalkyl groups together with polyester and polyether polyols having a molecular weight of &gt;700 for the production of polyurethanes. Aliphatic isocyanates are preferred. German Offenlegungsschrift No. 2,150,152 describes polyisocyanates obtained by reacting monohydroxyalkyl hydantoins and uracils with polyisocyanates, preferably in a stoichiometric ratio of 1:2. German Offenlegungsschrift No. 2,523,615 mentions the use of bishydroxyalkylated hydantoins, together with other cross-linkers and polyoxyalkylene polyols, combined with polyisotyanates as binders for foundry sand. U.S. Pat. No. 4,002,798 teaches that isocyanate-free compositions are obtained by reacting bis-hydroxyethyl hydantoin with an allyl alcohol and a diisocyanate and reacting the resulting polyene with a polythiol. Similar compositions are described in U.S. Pat. No. 4,017,650. According to German Offenlegungsschrift No. 2,750,722, hydantoins containing isocyanate groups may be obtained by subjecting the reaction product of an aminoalcohol and an unsaturated dicarboxylic acid ester to cyclization with a di- or polyisocyanate. The products are used for wire and electrical insulation lacquers.
However, it is not apparent from any of the prior publications mentioned above that isocyanate-group-containing prepolymers or semiprepolymers based on organic polyisocyanates and hydantoin derivatives containing alcoholic hydroxyl groups of the type used in the process of the present invention are compositions having a reduced melting point and a reduced tendency towards crystallization on storage at low temperatures and may be used with particular advantage in the production of polyurethane plastics, particularly polyurethane moldings having a homogeneous surface.